1. Field of the Invention
The present invention relates to a fuel supply apparatus for engines, which discharges fuel from a fuel tank by a fuel pump and controls the fuel pump to regulate pressure of the fuel.
2. Description of Related Art
One of the fuel supply apparatuses of the above type is disclosed in Japanese patent unexamined publication No. HEI 10-89184 (Patent Literature 1), on pages 2-9 and FIGS. 2-5. This fuel supply apparatus is designed to supply fuel from a fuel tank to a delivery pipe and injectors of an engine through a fuel pump and a fuel line. In this apparatus, the fuel pump is controlled by an electronic control unit (ECU) so that the pressure of fuel to be supplied to the injectors becomes the target pressure responsive to an operating state of the engine. This apparatus is not constructed to return the remaining fuel, which has been not injected through the injectors, to the fuel tank through the delivery pipe and hence it is not provided with a generally used return line and pressure regulator. Thus, the apparatus can have a simplified piping configuration.
Furthermore, the fuel tank of the above apparatus is shaped like a saddle having a concave portion opening into an underside so that the tank mounted in a vehicle does not interfere with a propeller shaft (not shown) or the like. The fuel tank is partitioned into a first and second storage chambers by the concave portion. The fuel pump is placed in only the first storage chamber and therefore cannot directly pump and discharge the fuel from the second storage chamber. This apparatus is accordingly provided with a branch passage through which a part of the fuel pumped from the first storage chamber by the fuel pump to be discharged into the fuel line is returned to the first storage chamber. On the branch passage ar disposed an electromagnetic valve for opening and closing the branch passage and a jet pump for letting fuel through the branch passage to produce a negative pressure in the branch passage. A communication passage is provided between the jet pump and the second storage chamber, providing a fluid communication therebetween. Accordingly, when the electromagnetic valve is opened, a part of the fuel discharged by the fuel pump is returned to the first storage chamber through the branch passage. When this return fuel passes through the jet pump, a negative pressure is formed in the pump. By the suction power resulting from the negative pressure, the fuel in the second storage chamber is transferred to the first storage chamber through the communication passage. In this apparatus, the electromagnetic valve of a normally opened type is controlled by the ECU to close in response to the operating state of the engine. For example, under acceleration when the engine demands a larger quantity of fuel (a target fuel pressure increases), the electromagnetic valve is closed upon energization, blocking the branch passage. Thus, the flow of fuel is stopped in the branch passage, so that the fuel pressure being supplied to the injectors increases by just that much.
Japanese patent publication No. 3,196,656 (Patent Literature 2) discloses, on pages 2-6 and FIGS. 2-4, a fuel supply apparatus including a mechanical structure identical to that of the fuel supply apparatus described in the patent literature 1. Moreover, Japanese patent publication No. 3,228,146 (Patent Literature 3) discloses, on pages 7-8 and FIG. 7, a fuel supply apparatus including a similar structure to those of the fuel supply apparatuses disclosed in the patent literatures 1 and 2. The fuel supply apparatus in the patent literature 3 uses a relief valve instead of the electromagnetic valve in the patent literatures 1 and 2.
In the fuel supply apparatus in the patent literature 1, when the quantity of fuel is reduced for deceleration of an engine or when the engine demands a relatively smaller quantity of fuel, the electromagnetic valve is opened to return the surplus fuel to the first storage chamber through the branch passage and the jet pump. At this time, the jet pump pumps the fuel from the second storage chamber to transfer the fuel to the first storage chamber.
In the fuel supply apparatus disclosed in the patent literature 2, when the engine increased in temperature is stopped, the electromagnetic valve is opened while the fuel pressure in the fuel line and the delivery pipe is increasing, thereby returning the fuel to the first storage chamber through the branch passage and the jet pump. At this time, the jet pump is also operated to pump the fuel from the second storage chamber into the first storage chamber.
In the fuel supply apparatus disclosed In the patent literature 8, when the pressure of fuel to be discharged by the fuel pump into the fuel line exceeds a setting pressure value, the relief valve is opened to return the fuel to the first storage chamber through the branch passage (the relief passage) and the jet pump. At this time, the fuel pressure in the fuel line decreases and simultaneously the fuel is pumped from the second storage chamber by suction power of the jet pump and transferred to the first storage chamber.
In the fuel supply apparatuses in the above patent literatures 1-3, the flow quantity of fuel to be transferred (a transfer flow quantity) from the second storage chamber to the first storage chamber depends on the quantity of fuel (a surplus flow quantity) flowing from the fuel line to the branch passage. This surplus flow quantity is determined by a difference between the quantity of fuel discharged from the fuel pump and the quantity of fuel injected from the injectors. The difference is unstable and sometimes excessive. If the surplus flow quantity becomes excessive, accordingly, the transfer flow quantity will become excessive. Thus, an excessive quantity of fuel may be returned from the jet pump to the first storage chamber, with a consequent fear that the fluid level of fuel in the first storage chamber is so undulated as to generate a large quantity of fuel vapors.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a fuel supply apparatus for engines, capable of preventing the generation of a large quantity of fuel vapors during fuel transfer from a storage chamber to a specific storage chamber.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a fuel supply apparatus comprising: a fuel tank for storing fuel, including a plurality of storage chambers one of which is a specific storage chamber; a fuel pump, placed in the specific storage chamber, for discharging the fuel from the fuel tank into a fuel passage which is communicated with an engine, the fuel pump being controlled to regulate pressure of the fuel which is to be supplied to the engine; a branch passage branching off of the fuel passage, through which branch passage a part of the fuel discharged by the fuel pump is returned to the specific storage chamber; a communication passage which provides communication between a storage chamber other than the specific storage chamber and the branch passage; transfer means for transferring the fuel from the storage chamber other than the specific storage chamber to the specific storage chamber through the communication passage by action of the fuel flowing through the branch passage; flow regulation means for regulating a flow quantity of fuel in the branch passage; fuel consumption calculation means for calculating a quantity of fuel to be sequentially consumed in the engine; and flow regulation control means for controlling the flow regulation means to transfer fuel in a quantity corresponding to the fuel consumption quantity calculated by the fuel consumption calculation means, from the storage chamber other than the specific storage chamber to the specific storage chamber through the communication passage.
According to another aspect, the present invention provides a fuel supply apparatus comprising: a fuel tank for storing fuel, including a plurality of storage chambers one of which is a specific storage chamber; a fuel pump, placed in the specific storage chamber, for discharging the fuel from the fuel tank into a fuel passage which is communicated with an engine including a plurality of cylinders, the fuel pump being controlled to regulate pressure of the fuel which is to be supplied to the engine; injectors for supplying the fuel, delivered thereto through the fuel passage, into respective associated cylinders; a branch passage branching off of the fuel passage, through which branch passage a part of the fuel discharged by the fuel pump is returned to the specific storage chamber; a communication passage which provides communication between a storage chamber other than the specific chamber and the branch passage; a jet pump for transferring the fuel from the storage chamber other than the specific storage chamber to the specific storage chamber through the communication passage by action of the fuel flowing through the branch passage, the jet pump including: a restricted portion for restricting a flow quantity of fuel in the branch passage; and a discharge port through which the fuel having passed through the restricted portion is discharged, the restricted portion being adapted to increase a flow velocity of the fuel passing through the restricted portion, producing a negative pressure in the restricted portion and a consequent suction power, so that the fuel is sucked from the storage chamber other than the specific storage chamber and transferred into the specific chamber through the communication passage and the discharge port; an electromagnetic valve for regulating the flow quantity of fuel in the branch passage, the electromagnetic valve including a valve body and energization of the electromagnetic valve being controlled to reciprocate the valve body between a full open position and a full closed position; fuel consumption calculation means for calculating a quantity of fuel to be sequentially consumed in the engine; and flow regulation control means for controlling the flow regulation means to transfer fuel in a quantity corresponding to the fuel consumption quantity calculated by the fuel consumption calculation means, from the storage chamber other than the specific storage chamber to the specific storage chamber through the communication passage, the now regulation control means calculating an energization time of the electromagnetic valve based on the fuel consumption quantity calculated by the fuel consumption calculation means and, based on the calculated energization time, operates the electromagnetic valve under a duty control at a predetermined cycle.